The present invention relates to a photosensitive member for electrophotography, and more particularly to a photosensitive member for electrophotography with excellent durability containing particular binder resins.
Since electrophotographic technology can provide instantaneous and high-quality images, it has been finding wider applications not only in copiers but also in various types of printers.
For photosensitive members which are the core of the electrophotographic technology, conventional inorganic photoconductive materials such as selenium, arsenic-selenium alloys, cadmium sulfide, zinc oxide, etc. are being used, and recently development has been made to provide photosensitive members made of organic photoconductive materials because of their advantages such as small weight, good film-forming properties and easiness to production.
Known as organic photosensitive members are double layer-type photosensitive members having a charge carrier-generating layer and a charge carrier transfer layer on a conductive substrate. Since this type is enjoying high sensitivity and durability, it is widely used.
However, despite the fact that the conventional organic, double layer-type photosensitive members have good electric properties such as sensitivity and chargeability, they are susceptible to mechanical wear and surface damage by such load as abrasion by a cleaning member. The surface wear and damage of a photosensitive member leads to deteriorated copy or print images. Therefore, they have only limited durability when actually used in copiers or printers.
Conventionally used for charge carrier transfer layers as binder resins are thermoplastic resins such as polycarbonate resins, acrylic resins, methacrylic resins, polyester resins, polystyrene resins, silicone resins, epoxy resins, polyvinyl chloride resins, etc., and various curable resins. Usually, the charge carrier transfer layer is made of a solid solution of the binder resin and a charge carrier transfer material, and the amount of this charge carrier transfer material doped is considerably large. Thus the charge carrier transfer layer does not have a sufficient surface strength. As a result, when it is used for a process employing a blade cleaning method, it provides images deteriorated by surface abrasion wear and damage after producing several thousands to about ten thousand of copies, making it inevitable to exchange the photosensitive member.
Among these binder resins, polycarbonate resins have relatively good mechanical properties, so that they enjoy relatively good durability. However, commercially available polycarbonate resins which are usually employed have poor solution stability because they are crystalline. Accordingly, although it provides a uniform solution in the initial stage, crystallization gradually takes place, resulting in the increase in gelation with time. When such solution is applied for preparing a photosensitive layer, a uniform layer is hard to obtain, resulting in low productivity of the photosensitive layer. In addition, the photosensitive members containing commercially available polycarbonate resins as binders are still unsatisfactory in terms of mechanical durability.
In addition to the above double layer-type photosensitive member, a proposal has recently been made to provide a so-called dispersion-type (single layer-type) photosensitive member having a binder resin-containing layer having a charge carrier transfer function, in which charge carrier-generating material particles are dispersed. Like the double layer-type photosensitive member, this dispersion-type photosensitive member suffers from surface damage and wear due to a mechanical load during the use. Accordingly, the binder resin used is required to have sufficient strength, and its solution for application should be stable. Particularly in this type, the dispersion stability of charge carrier-generating material particles is important. However, as in the above-mentioned double layer-type photosensitive member, commercially available polycarbonate resins have insufficient strength, and their solutions for forming photosensitive layers are poor in stability.